CNS complications of HIV infection remain a serious risk in HIV-1 infection despite significant advances in highly active antiretroviral therapy. Our research is based on a general hypothesis that specific HIV proteins, such as Tat, contribute to the dysfunction of brain microvascular endothelial cells (BMEC) and the disruption of the blood-brain barrier (BBB), facilitating virus entry into the brain. The present grant application is designed to study the signaling mechanisms that can be responsible for these effects. Our recent preliminary data indicate that exposure of endothelial cells to Tat results in immediate localization of Tat to caveolae, the subset of lipid rafts characterized by the presence of proteins termed caveolins. The importance of this observation is related to the fact that a variety of cell surface receptors and signaling pathways activated by Tat are also localized in these membrane domains. In addition, we demonstrate that silencing of caveolin-1 protein can protect against Tat-mediated toxicity to BMEC. Based on our preliminary data, we propose that caveolae provide the signaling platform detrimental for vascular toxicity of Tat. We hypothesize that Tat-induced alterations of caveolae-associated pathways, such as the Ras and Rho signaling cascades, are the underlying mechanisms of Tat-induced injury to BMEC and disruption of the BBB. Mechanistically, we propose that Tat-induced alterations of the Ras and Rho signaling pathways result in disturbances in tight junction protein expression, leading to increased transendothelial passage of inflammatory cells and HIV entry into the brain. We also propose that statins can regulate caveolae-associated signaling and protect against Tat- mediated vascular toxicity. This project is interdisciplinary and combines molecular and vascular biology with pro- clinical approaches. It is based on the newly developed co-cultures of human brain microvascular endothelial cells (HBMEC) with genetically altered human astrocyte cell lines that produce Tat (SVGA-Tat cells). This proposal is the first attempt to study the role of functional caveolae in the regulation of the BBB in relationship to HIV-1 infection. Data arising from this proposal will be critical for a better understanding of the development of the BBB dysfunction in neuroAIDS. The long term goals of this proposal are to determine therapeutic strategies to prevent neurological complications of HIV infection. RELEVANCE Dysfunction of the blood-brain barrier and brain endothelial cells contribute to HIV-1 trafficking into the brain and the development of HIV-1-associated neurotoxicity. We hypothesize that HIV-1 protein Tat can contribute to this pathology through stimulation of caveolae-associated pathways. This proposal is the first attempt to study the role of functional caveolae in the regulation of the blood-brain barrier in relationship to HIV-1 infection.